1. Technical Field
The present invention relates in general to patterning magnetic media for hard disk drives and, in particular, to an improved system, method and apparatus for hard disk drive patterned magnetic media having a reduced amount of magnetic trench material.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic storage media. For example, a magnetic storage device or hard disk drive (HDD) includes one or more disks and a disk controller to manage operations concerning the disks. The hard disks themselves are usually fabricated from an aluminum alloy, glass or a mixture of glass and ceramic, and are covered with a magnetic media coating that contains the bit pattern.
One common approach to making the bit patterned media (BPM) or discrete track media (DTM) on the disks is to create topographic patterns on the substrate, followed by blanket deposition of the magnetic recording layers. Magnetic material deposited on the tops (or “lands”) of topographic features is used for recording, while material deposited in the etched relief areas (or “trenches”) is not intended to be used for recording.
However, it has been shown through both modeling and experiments that magnetic material located in the trenches produces significant unwanted magnetic flux, which interferes with the readback signal. The present invention seeks to reduce the amount of magnetic material ending up in the trenches and thereby to reduce readback interference caused by the trench material.
Referring to FIG. 1, a schematic sectional side view of a disk 11 having conventional patterned media formed on a substrate 13 is shown. The media includes a soft underlayer 15, an exchange break layer 17 and non-magnetic pillars 19 or raised track structures having trenches 25 therebetween. A magnetic layer is blanket deposited on the topographically patterned substrate. This deposition forms a magnetic recording layer 21 (i.e., formed as “islands”) on the pillars 19, and some magnetic material 23 in the trenches 25 between the pillars 19. The magnetic material 21 deposited on top of the pillars 19 is used for recording, while the trench material 23 generates unwanted magnetic flux that increases the background noise level and interferes with readback operations of the disk drive.
The amount of magnetic material in the trenches can be reduced by depositing the magnetic material at an angle with respect to normal incidence. However, angled deposition does not completely eliminate the trench material due to the complex, three-dimensional shapes of the pillars (particularly for BPM), and the fact that sputter deposition has only limited directionality. Furthermore, angled deposition can result in significant deposits on the sidewalls of the topography, which also has unintended effects on the magnetic properties of the islands or tracks.
An alternative solution to this problem is to “poison” the trench material. Poisoning the trench material is attractive from the point of view of totally eliminating the magnetism of the trench material. However, there are some challenges to successfully implementing such an approach for small feature sizes, including the effects of dimensional distortion of feature shapes due to diffusion processes. Thus, an improved solution for reducing the unwanted effects of having magnetic media located in the trenches between the topographic features of disks would be desirable.